Field of the Invention
The subject of this invention is a device for measuring the internal profile of a hollow shaft, which makes it possible to measure the radius irregularities of the hollow of this shaft over successive circumstances.
Description of the Related Art
Such measurements are taken on turbomachine rotor shafts, generally concurrently to measurements of the outer profile, in such a way as to in particular know the concentricity of the outer and inner surfaces of these shafts.
Certain difficulties with these measurements stem from the necessity of their precision and of the great length of the shafts. Sensors without contact with the surface of the blade are generally preferred, in order to avoid possibilities of errors dues to forces of contact and deformations. The shaft must be in a non-deformed condition, in such a way that it is attached vertically to a frame, and the measurements are therefore taken by progressively pushing the sensor into the hollow, after having raised it above the upper end of the shaft. In prior art, the sensor is attached to the lower end of a tubular rod, able to be made of carbon and which is slide into the hollow of the shaft. It is however difficult to guarantee the absence of deformations of the rod, and therefore the absence of measurement errors stemming from an incorrect radial position of the sensor. Another disadvantage that is encountered is that the rod must be at least as long as the shaft and must be lifted above it in order to introduce the sensor, which results in substantial vertical encumbrance of the whole.
The difficulties are more substantial with certain thin and long shafts (2.5 m, for example), which are now proposed in certain machines: the vertical encumbrance of the whole is obviously increased, and it is becoming genuinely difficult to design a rod that remains rigid enough, especially at the finesse to which it is restricted. It is to obviate these difficulties that the invention was designed. It consists in replacing the support and guide rod with another device that is more convenient and less massive and bulky, but paradoxically more rigid.